CN109809722B - Calcium-magnesium sulfate double-salt cementing material and preparation method and application thereof - Google Patents

Calcium-magnesium sulfate double-salt cementing material and preparation method and application thereof Download PDF

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CN109809722B
CN109809722B CN201910270626.7A CN201910270626A CN109809722B CN 109809722 B CN109809722 B CN 109809722B CN 201910270626 A CN201910270626 A CN 201910270626A CN 109809722 B CN109809722 B CN 109809722B
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magnesium
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double salt
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CN109809722A (en
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邓德华
吴晓燕
元强
刘赞群
李柯
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Central South University
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Abstract

A calcium sulfate magnesium double salt cementing material and a preparation method and application thereof; the double-salt cementing agent comprises the following components: calcium sulfate magnesium double salt, active magnesium oxide and mineral powder; the calcium sulfate magnesium double salt is desulfurized calcium sulfate magnesium double salt powder discharged in the kiln flue gas desulfurization process, or waste acid calcium sulfate magnesium double salt powder formed by treating industrial waste sulfuric acid with dolomite, or gypsum-based calcium sulfate magnesium double salt powder obtained by thermally dehydrating industrial byproduct gypsum raw slag in the presence of magnesium sulfate; other mineral powders include fly ash, limestone powder, dolomite powder, building gypsum, and the like. The invention not only provides a new technology for economically and efficiently utilizing flue gas desulfurization products, industrial waste sulfuric acid and phosphogypsum, but also the prepared double-salt cementing material has excellent physical and mechanical properties, and has the outstanding characteristics of quick condensation, high strength and good water resistance, and multiple social benefits of environmental protection, economy, new materials and the like are obtained. The preparation method of the calcium sulfate magnesium double salt cementing material is simple and easy to implement and has low energy consumption.

Description

Calcium-magnesium sulfate double-salt cementing material and preparation method and application thereof
Technical Field
The invention relates to a calcium sulfate magnesium double salt cementing material, a preparation method and application thereof, belonging to the field of inorganic cementing materials and building materials.
Background
In the field of inorganic binders, there are generally two categories, hydraulic and hydraulic binders. Commercial cements such as portland cement, aluminate cement and sulphoaluminate cementBelonging to hydraulic cementing materials; various building plasters belong to the air-setting cementitious materials. The essential differences are: the main hydrates of hydraulic binders are highly stable in water, so that such cement-and water-mixed slurries can develop in water and retain their microstructure and physico-mechanical properties; the water stability of the major hydrates of air-setting cements is poor and soluble, so that these cements and water-stirred slurries develop and retain their microstructure and physicomechanical properties only in dry air. Various cements have good engineering properties such as setting and hardening, strength and durability, and are widely used for various infrastructure constructions, but the manufacturing process of the cement consumes a large amount of energy and also discharges a large amount of CO2Gas, polluting the atmosphere. For example, Portland cement with the highest global production energy, which accounts for 3% of the total global energy consumption, CO2The gas emission accounts for 5 percent of the total global amount (about 0.87 ton of CO is emitted when 1 ton of cement is produced2Gas). Therefore, in order to protect the ecological environment of the earth, low-carbon and low-energy consumption cement (cement) or cementing material (binder) and new manufacturing technology thereof are sought in all countries in the world. For example, chinese patent CN201610841814.7 discloses a method for reducing CO by using phosphogypsum to replace limestone to fire sulphoaluminate cement clinker2The technical proposal of the gas discharge is that,
the production energy consumption of the building gypsum is low, and hardly any harmful gas is generated, because the main gelled substance of the building gypsum is beta-type calcium sulfate hemihydrate generated by heating and dehydrating calcium sulfate dihydrate at 120-180 ℃. On the other hand, besides natural gypsum can be used as a source of calcium sulfate dihydrate, flue gas desulfurization gypsum and industrial by-product gypsum such as phosphogypsum, titanium gypsum, mirabilite gypsum, fluorgypsum, citric acid gypsum and the like also use calcium sulfate dihydrate as a main component. 1.7 million tons of industrial by-product gypsum is produced in our country in about one year, and can be used for manufacturing building gypsum after being properly treated, so the building gypsum is a cementing material with low carbon and low energy consumption. Unfortunately, building gypsum is an air-setting cement, and the strength of the hardened gypsum slurry is low, and the calcium sulfate dihydrate crystal generated by the setting reaction has high water solubility and cannot maintain the geometric shape and the physical and mechanical properties in water or a humid environment. Thus, the use of construction gypsum in civil engineering and construction work is very limited. This results in the comprehensive utilization rate of the industrial by-product gypsum being less than 30%, that is, about 1.2 million tons of industrial by-product gypsum are stacked and stored every year, which not only causes resource waste, but also causes the industrial by-product gypsum to contain some soluble acidic substances, which pollute the water and soil environment during stacking and storage. Therefore, how to improve the mechanical property and the water resistance of the cementing material taking calcium sulfate as a main phase is a technological problem in the field of inorganic cementing materials; comprehensive treatment and utilization of industrial by-product gypsum are technological problems in the fields of ecological environment protection and resource utilization, and for this reason, various countries seek principles and technologies for utilizing calcium sulfate or industrial by-product gypsum-based novel cementing materials. The calcium sulfoaluminate cement invented in 1975 of China is an example of producing high-strength and water-resistant hydraulic cement by utilizing calcium sulfate, for example, Chinese patent CN97116488.6 discloses a scheme for producing quick-hardening low-alkalinity calcium sulfoaluminate cement by utilizing phosphogypsum to replace natural gypsum, and the phosphogypsum accounts for 30-40% of the mass of the cement. However, the production of sulphoaluminate cement requires high-grade bauxite as a key raw material, and the bauxite is not only an important raw material in the alumina and electrolytic aluminum industries, but also has low storage capacity and less distribution area, so that the popularization and the application of the technical invention are greatly limited. Chinese patent CN201610034309.1 discloses a technical scheme for preparing low-carbon cement clinker by using low-grade bauxite, but the proportion of calcium sulfate in the cement is less than 15 percent. Therefore, how to produce the low-carbon and low-energy-consumption cementing material by using the calcium sulfate as the main raw material is still a difficult problem.
In the field of atmospheric environmental protection, researches show that SO in kiln flue gas of coal-fired power plants and steel smelting plants2、NOxAnd inhalable particles and the like are the origin of fog and haze weather, and if harmful gases in smoke are solidified and effectively utilized, huge resources can be obtained, and the atmospheric environment can be protected. By SO in flue gas2For example, our country consumes about 40 million tons of raw coal each year, has about 8.08 million tons of crude steel production, and produces about hundred million tons of SO each year2A gas. If passing through the flue gas desulfurization process, the SO in the flue gas2The gas is converted to sulfate and hundreds of millions of tons of sulfate-based solids or suspended slurry can be produced.
Flue gas desulfurization refers to the removal of Sulfur Oxides (SO) from industrial kiln flue gas or other industrial waste gases2And SO3) The process of (1) according to the type of the desulfurizer, five existing flue gas desulfurization process methods are as follows: from limestone (CaCO)3)、Ca(OH)2Or calcium method using CaO as desulfurizing agent, using magnesite (MgCO)3) Light-burned magnesium oxide (MgO) or Mg (OH)2Magnesium method using sodium carbonate (Na) as desulfurizing agent2CO3) Sodium method using sodium hydroxide (NaOH) as desulfurizing agent, ammonia gas (NH)3) And ammonium hydroxide (NH)4OH) and the like, and an organic base method using an organic base as a desulfurizing agent. The state of the absorbent and desulfurization products during desulfurization can be classified into wet, dry, semi-dry or semi-wet. Among the five flue gas desulfurization methods, two desulfurization methods, namely a wet calcium method and a wet magnesium method, are widely adopted by countries in the world based on the consideration of technical maturity, cost and desulfurization efficiency. More than 90% of coal-fired power plants, steel plants and 87% of coal-fired power plants in America adopt wet calcium method process. The process uses limestone (CaCO)3) Lime (CaO) or sodium carbonate (Na)2CO3) The slurry is used as a washing agent to wash the flue gas in a reaction tower SO as to ensure that SO in the flue gas2And SO3The gas is converted into desulfurized gypsum (calcium sulfate dihydrate) for removal. However, in the calcium desulphurization method, the desulfurized gypsum is easy to scale and block, so that a desulphurization unit is difficult to stably operate for a long time, and for example, the blockage and shutdown failure rate of a desulphurization device of a coal-fired power plant in China is reported to be as high as 48.8%. In countries and regions with early desulfurization treatment such as Japan and Taiwan, more than 95% of coal-fired power plants adopt wet magnesium method for desulfurization, and more than ten large coal-fired power generating sets and steel enterprises in mainland China adopt wet magnesium method. The process uses light-burned magnesia slurry as a washing agent to wash the flue gas in a reaction tower SO as to ensure that SO in the flue gas2And SO3The gas was converted to magnesium sulfate solution and removed. Removing with calcium methodCompared with a sulfur process, the magnesium desulfurization efficiency is up to more than 95-98%, and the calcium desulfurization efficiency is about 90%; the magnesium sulfate is dissolved in water and is easy to discharge, the investment of the desulfurization equipment is reduced by more than 20%, the operation cost is low, and the long-term reliability is realized. However, the magnesium desulphurization process also has two defects, one is that the unit price of light-burned magnesium oxide (MgO) is higher, and the magnesite ore as a production raw material is limited by the national mineral resource protection policy; and secondly, the magnesium sulfate aqueous solution discharged from the desulfurizing tower needs to be purified by a pretreatment device, an evaporation device, a crystallization device and a drying device to prepare the industrial magnesium sulfate heptahydrate (Chinese patent CN201720755781.4), so that the cost is high and the application range is limited. Therefore, the actual utilization rate of the magnesium desulfurization product is low, and most of the magnesium desulfurization product is discharged, thereby causing resource waste and water and soil environmental pollution. Therefore, the wet magnesium process desulfurization should be popularized and used based on the consideration of desulfurization efficiency and long-term operation rate of equipment, but the two problems that magnesium oxide resources and the utilization problem of magnesium sulfate generated by desulfurization are required to be solved are solved.
The invention provides a method for replacing magnesite with dolomite, which solves the problem of magnesium oxide resource. Dolomite is a double salt of calcium carbonate and magnesium carbonate [ CaMg (CO)3)2]Theoretically, dolomite contains 30.41% CaO, 21.83% MgO and 47.73% loss on ignition (CO)2). When the temperature is lower (650-750 ℃), dolomite is half decomposed to generate active magnesium oxide MgO and calcium carbonate (CaCO)3) When the temperature is higher (850-950 ℃), dolomite is decomposed completely to generate active magnesia MgO and quicklime (CaO). Therefore, the wet calcium method and the magnesium method are combined together, dolomite powder or slurry of light burned dolomite powder is used as a washing agent, and the flue gas is washed in a reaction tower, SO that SO in the flue gas2And SO3Gas with MgO, CaO, CaCO3And MgCO3Reacting, converting into mixed slurry formed by calcium sulfate dihydrate and high-concentration magnesium sulfate or magnesium sulfite solution, discharging, reducing or eliminating the deposition and blockage of calcium sulfate in calcium desulphurization, causing the unstable operation of equipment, removing sulfur oxide gas from flue gas, and generating magnesium sulfate and calcium sulfate double salt. In fact, Chinese patent CN200910019038.2 discloses a technical scheme of a desulfurization process for coal slime mixed with burned dolomite, and the problem of recycling is solvedHigh desulfurization cost of the circulating fluidized bed, unstable desulfurization efficiency and the like. The coal slag discharged by the desulfurization process contains calcium sulfate and magnesium sulfate double salts and should be efficiently utilized.
In the chemical industry, sulfuric acid is widely used in industrial processes, and thus, the total amount of waste sulfuric acid discharged is huge, and it is estimated that the amount of waste sulfuric acid discharged at different concentrations per year is huge (at 100% H)2SO4In the order of 1500 ten thousand tons). Although some technical schemes and equipment for recycling the waste sulfuric acid exist, the industrial waste sulfuric acid has the characteristics of complex impurity components, high treatment cost, large total amount and dispersed industry, and brings great difficulty for recycling and harmless treatment. For some industrial waste sulfuric acid without recovery value, if the industrial waste sulfuric acid is treated by adopting a dolomite neutralization method, H in the waste sulfuric acid is caused2SO4And reacting with dolomite to generate calcium sulfate and magnesium sulfate double salt, thereby realizing resource recovery of sulfur in the waste sulfuric acid.
The invention also provides a technical scheme that a novel high-strength waterproof double-salt cementing material is invented by adopting a dolomite desulfurization process and a double salt of magnesium sulfate and calcium sulfate generated in the treatment of waste sulfuric acid by dolomite as main raw materials, so that the problems of resource utilization and ecological environment protection of sulfur-containing industrial waste gas, waste residue and waste water are solved.
Disclosure of Invention
In order to efficiently recycle industrial by-product gypsum, dolomite desulfurized slag and waste sulfuric acid for manufacturing low-carbon and low-energy-consumption inorganic cementing material, the invention aims to provide the calcium sulfate magnesium cementing material and the preparation method and the application thereof; the invention takes industrial by-product gypsum, magnesium salt produced by magnesium desulphurization, dolomite desulphurization and solid produced by neutralizing waste sulfuric acid as important raw materials to prepare the double-salt cementing material with excellent service performance, and opens a new way for economic and efficient resource utilization of some industrial by-products.
The invention relates to a calcium sulfate magnesium double salt cementing material, which comprises the following components in parts by mass:
50-250 parts of calcium sulfate and magnesium sulfate double salt; 40-200 parts of active magnesium oxide; 50-300 parts of mineral powder.
The preferred components are:
50-180 parts of calcium sulfate and magnesium sulfate double salt; 50-180 parts of active magnesium oxide; 60-250 parts of mineral powder.
More preferred components are:
60-150 parts of calcium sulfate and magnesium sulfate double salt; 50-150 parts of active magnesium oxide; 80-200 parts of mineral powder.
The invention relates to a calcium sulfate magnesium double salt cementing material, wherein the calcium sulfate magnesium double salt is selected from one or two of calcium sulfate magnesium physical double salt and calcium sulfate magnesium chemical double salt, and the two are mixed according to any mass ratio during compounding.
The invention relates to a calcium sulfate magnesium double salt cementing material, wherein mineral powder is selected from at least one of fly ash, limestone powder, dolomite powder and building gypsum.
The invention relates to a calcium magnesium sulfate double salt cementing material, wherein the calcium magnesium sulfate physical double salt comprises xCaSO4·yMgSO4·zH2O, wherein in the formula, the (x/y) is more than or equal to 1 and less than or equal to 3, and the z is more than or equal to 1 and less than or equal to 3.
The invention relates to a calcium magnesium sulfate double salt cementing material, which is prepared by the following method:
mixing industrial byproduct gypsum raw slag and magnesium sulfate, heating to 120-360 ℃ for dehydration, and physically combining calcium sulfate dihydrate in the raw slag with the magnesium sulfate to generate physical double salt xCaSO of calcium sulfate and magnesium sulfate4·yMgSO4·zH2O; grinding and sieving to obtain physical double salt solid powder with the average particle size of 0.1-50 mu m; or
Mixing dolomite [ CaMg (CO) ]3)2]Adding the powder into an industrial waste sulfuric acid solution with the mass concentration of 30-70%, and stopping the reaction until the pH value of the mixture is 4-6; the mixture is dehydrated at 120-360 ℃ after free water is evaporated to generate a physical double salt xCaSO of calcium sulfate and magnesium sulfate4·yMgSO4·zH2O; grinding and sieving to obtain physical double salt solid powder with the average particle size of 0.1-50 mu m; or
Removing SO in flue gas of industrial kiln by using dolomite, light-burned dolomite or calcined dolomite2Gas, resulting mixture of calcium sulfate and magnesium sulfateDehydrating the mixed slurry at 120-360 ℃ to generate a calcium magnesium sulfate physical double salt xCaSO4·yMgSO4·zH2O; grinding and sieving to obtain the physical double salt solid powder with the average particle size of 0.1-50 mu m.
The industrial by-product gypsum raw slag is at least one of phosphogypsum, titanium gypsum, citric acid gypsum, fluorgypsum, mirabilite gypsum and calcium desulfurization gypsum which are not subjected to any purification or deacidification treatment.
The invention relates to a calcium sulfate magnesium double salt cementing material, wherein the calcium sulfate magnesium chemical double salt comprises Mg2Ca(SO4)3
The invention relates to a calcium sulfate magnesium double salt cementing material, wherein the calcium sulfate magnesium chemical double salt is prepared by directly selecting ash slag discharged from a pressurized fluidized bed combustion furnace of a coal slime doped dolomite desulfurization process or calcining calcium sulfate magnesium physical double salt at 725-950 ℃.
The calcium sulfate magnesium double salt cementing material has the average particle size of 0.1-50 microns.
The invention relates to a calcium magnesium sulfate double salt cementing material, wherein the active magnesium oxide is selected from magnesite (MgCO)3) The light-burned magnesia powder is prepared by calcining and grinding the raw materials, and comprises more than 50 percent of active MgO and less than 1.5 percent of free CaO, the ignition loss is less than 12 percent, and the average particle size is 0.1-50 mu m.
The invention relates to a calcium-magnesium sulfate double salt cementing material, which is characterized in that active magnesium oxide is selected from dolomite ore (CaCO)3·MgCO3) The light calcined dolomite powder is prepared by calcining and grinding the raw materials, and comprises the components of more than 20 percent of active MgO, less than 2.5 percent of free CaO, the ignition loss is more than about 40 percent, and the average particle size is 0.1-50 mu m.
The invention relates to a preparation method of calcium sulfate magnesium double salt cementing material powder, which comprises the following steps: and (3) preparing each component of powder according to the designed component formula of the double-salt cementing material, and mixing for 4-8 minutes at the rotating speed of 60-100 revolutions per minute by using a dry powder mixer to uniformly mix the component of powder to obtain the double-salt cementing material powder.
In the components of the double-salt cementing material, the physical double salt of calcium sulfate and magnesium sulfate and the chemical double salt are added independently or mixed; the active magnesium oxide is selected from one or a mixture of two or more than two of light-burned magnesium oxide powder, light-burned dolomite powder or industrial active magnesium oxide.
The invention relates to a preparation method of calcium sulfate magnesium double salt cementing material slurry, which comprises the following steps: preparing powder of each component according to a designed formula of the components of the double-salt cementing material; metering and pumping clear water into a stirrer; adding the prepared powder of each component of the double-salt cementing material into a stirrer, and uniformly stirring at the rotating speed of 100-120 r/min to obtain the calcium sulfate magnesium double-salt cementing material slurry.
The invention relates to an application of a calcium-magnesium sulfate double salt cementing material, which is characterized in that slurry of the calcium-magnesium sulfate double salt cementing material is mixed with mineral powder and fiber, uniformly stirred and molded to form a blank, and the blank is coagulated and hardened at normal temperature or in an environment below 100 ℃ to prepare products used in the fields of buildings, building materials and other industries; the mineral powder is at least one of limestone powder, dolomite powder and talcum powder; the fiber is at least one of glass fiber, PVA fiber and PP fiber; the molding is realized by adopting the modes of pouring, extruding and rolling through a designed die.
The principle and the advantages of the invention are as follows:
the slurry formed by mixing the building gypsum with water is Ca2+-SO2--H2O ternary system, the phase in the hardened gypsum slurry is calcium sulfate dihydrate CaSO4·2H2O, its solubility in normal temperature water is large, about 2.05 g/L. Therefore, the set gypsum cannot develop in water and maintain its appearance and physical and mechanical properties. On the other hand, the hardened gypsum slurry microstructure is a network formed by the intergrowth and interaction of calcium sulfate dihydrate crystals with high porosity, and the strength of the crystals is low because the interaction force between the crystals is small.
The invention relates to a calcium-magnesium sulfate double salt cementing material, which consists of calcium-magnesium sulfate double salt and active magnesium oxide, wherein the slurry formed by mixing the calcium-magnesium sulfate double salt with water is Ca2+-Mg2+-SO2--OH--H2And an O quinary system. The dissolution of active magnesium oxide raises the pH value of the five-element system to trigger two alkaline earth metal cations Ca2+、Mg2+And SO2-、OH-The anions are subjected to sol-gel-crystallization and other complex physicochemical processes to generate novel sulfuric acid double salt hydrate crystals of which the compositions are to be carefully examined. Experimental studies have shown that, due to the intergrowth and interweaving of the novel sulfate double salt hydrate crystals, a dense microstructure (see fig. 1) is gradually established in the slurry to coagulate and harden and develop a very high strength; on the other hand, these hydrate crystals and the microstructures of their constituents are stable in water (see FIG. 2). Therefore, the hardened calcium magnesium sulfate double salt cementing material has the characteristics of being solidified and hardened in air and developing the strength thereof, and being capable of keeping the appearance and the physical and mechanical properties for a long time in water. Therefore, the calcium sulfate magnesium double salt cementing agent of the invention is not only different from hydraulic cementing material-cement which can develop strength in water, but also superior to air-hardening cementing material-building gypsum which has lower strength and loses the strength in water, and the compression strength and the breaking strength of the building gypsum are several times or even more than ten times of the building gypsum, thus being a novel air-hardening waterproof cementing material. The invention is a scientific, advanced and novel technical principle.
The invention not only provides a novel cementing material with excellent physical and mechanical properties, low carbon and low energy consumption for civil and architectural engineering construction, but also can efficiently utilize industrial byproduct gypsum, industrial waste sulfuric acid and flue gas desulfurization products in a resource manner, and obtains multiple social and economic benefits of energy conservation and emission reduction, waste material treatment and efficient utilization and ecological environment protection.
Description of the drawings:
FIG. 1 is a scanning electron micrograph of a hardened slurry specimen prepared in example 5 of the present invention.
FIG. 2 is an x-ray diffraction pattern of samples prepared in example 6 and example 12 of the present invention after curing. .
As can be seen from FIG. 1, the fibrous crystals having a relatively large major diameter form the microstructure of the hardened slurry of the calcium magnesium sulfate double salt cement.
In FIG. 2, Curve 1 is the x-ray diffraction pattern of the sample prepared in example 6 after being cured in air for 28 days; curve 2 is the x-ray diffraction pattern of the sample prepared in example 12 after immersion in water for 28 days; the composition ratios of both curves 1 and 2 are the same, and both curves show that they have the same crystal phase composition, indicating that the hydrate crystals do not change after 28 days of immersion.
Detailed Description
The implementation of the invention and the excellent properties of the calcium-magnesium sulfate double-salt cementing material are described below by specific examples, but the scope of the invention should not be limited thereby.
Comparative example 1
The desulfurized gypsum raw slag containing free water is randomly collected from a desulfurized gypsum storage pool discharged from a calcium method desulfurizing tower of a certain coal-fired power plant, and the main mineral of the desulfurized gypsum raw slag is calcium sulfate dihydrate (CaSO)4·2H2O) and contains small amounts of other oxides. Dehydrating the raw slag by heating in an open environment at 120-180 ℃, and passing the dehydrated raw slag through a 0.075mm square-hole sieve to obtain the desulfurized building gypsum powder, wherein the main component of the desulfurized building gypsum powder is beta type calcium sulfate hemihydrate (beta-CaSO)4·0.5H2O)。
100 parts of desulfurized building gypsum and 65 parts of water are mixed to form uniform slurry, the slurry is injected into cube and prism steel test molds, the mold is demolded after curing for 1 day in an environment with the temperature of 25 +/-2 ℃, test pieces are cured in air with the temperature of 25 +/-2 ℃ and the relative humidity of 65%, and the strength of the curing is respectively tested for 3 days (d), 7 days, 15 days and 28 days, and the results are shown in Table 5.
TABLE 1 chemical composition of desulfurized building gypsum
Chemical composition β-CaSO4·0.5H2O MgO SiO2 Al2O3 Others
Content/% 91.56 1.53 3.46 1.35 2.10
Examples 1 to 3
The calcium magnesium sulfate double salt cementing material powder in the embodiments 1 to 3 is formed by mixing calcium magnesium sulfate physical double salt, light-burned magnesia powder and limestone powder, and the design ratio of each component is shown in table 2; the calcium sulfate magnesium physical double salt is powder prepared by heating and dehydrating desulfurized dihydrate gypsum discharged by a calcium desulphurization process and magnesium sulfate heptahydrate generated by a magnesium desulphurization process in an open environment at 120-180 ℃, grinding solids and sieving the ground solids by a 0.075mm square-hole sieve; the light burned magnesium oxide was purchased from a certain enterprise in the sea city of Liaoning province and its chemical composition is shown in Table 3.
Table 2 composition and mixing ratio of physical double salt cements in examples 1 to 3
TABLE 3 chemical composition of light-burned magnesium oxide
Chemical composition MgO Active MgO CaO SiO2 Al2O3 Fe2O3 Loss on ignition
Content/% 85.0 65.0 1.30 3.09 0.16 0.33 10.03
In order to test the strength of the calcium sulfate magnesium double salt cements in examples 1 to 3, the three powders and water were mixed into slurry of double salt cement using a water-to-solid ratio of 0.4, and the slurry was uniformly mixed, and then injected into cubic and prismatic steel test molds, and after curing at 25 ℃. + -. 2 ℃ for 1 day, the molds were demolded, and then filled into plastic bags and further cured at 25 ℃. + -. 2 ℃, and the strength of the cured product was measured for 3 days (d), 7 days, 15 days, and 28 days, respectively, and the test results are shown in Table 5.
Examples 4 to 6
The calcium magnesium sulfate double salt cementing material powder in the embodiments 4 to 6 is formed by mixing calcium magnesium sulfate physical double salt and light-burned magnesia powder, and the design mixture ratio of each component is shown in table 4; wherein, the calcium magnesium sulfate physical double salt is powder prepared by heating and dehydrating phosphogypsum raw slag discharged by certain phosphorus chemical enterprises and magnesium sulfate heptahydrate generated by a magnesium desulphurization process in an open environment at 120-180 ℃, grinding solids and sieving the solids by a 0.075mm square-hole sieve; the lightly calcined magnesia was the same as in example 1.
In order to test the strength of the calcium sulfate magnesium double salt cements in examples 4 to 6, the three powders and water were mixed into slurry of double salt cement using the water-to-solid ratios of 0.55, 0.41 and 0.39, respectively, the slurry was uniformly mixed, poured into cubic and prismatic steel test molds, cured at 25 ℃. + -. 2 ℃ for 1 day, demolded, filled into plastic bags and cured at 25 ℃. + -. 2 ℃ for 3 days (d), 7 days, 15 days, 28 days and 60 days, respectively, and the test results are shown in Table 5.
Table 4 compositions and proportions of physical double salt cements in examples 4 to 6
Table 5 results of strength test of hardened cement slurry test pieces in comparative example 1 to example 6
Examples 7 to 9
The calcium magnesium sulfate double salt cement powders of examples 7 to 9 are prepared from calcium magnesium sulfate chemical double salt [ Mg2Ca(SO4)3]The light-burned magnesia powder and the desulfurized building gypsum are mixed, and the design proportions of the components are shown in Table 6; wherein, the calcium sulfate magnesium chemical double salt is powder prepared by burning desulfurized dihydrate gypsum discharged by a calcium desulphurization process and magnesium sulfate heptahydrate generated by a magnesium desulphurization process in a high-temperature furnace at 725-750 ℃, grinding cooled solids and sieving the ground solids by a 0.075mm square-hole sieve; desulfurized building gypsumSame as comparative example 1; the soft-burned magnesia powder was the same as in example 1.
Table 6 composition and mixing ratio (parts by mass) of the chemical double salt cements in examples 7 to 9
Examples Chemical double salt of calcium and magnesium sulfate Activated magnesium oxide Desulfurized building gypsum
Example 7 106.8 140 180
Example 8 106.8 127 200
Example 9 106.8 112 215
The three double salt cements of examples 7-9 were mixed with water to form a uniform slurry at a water-to-solid ratio of 0.49, and then poured into cubic and prismatic steel test molds, cured at 25 ℃. + -. 2 ℃ for 1 day, demolded, and filled into plastic bags and cured at 25 ℃. + -. 2 ℃ for 1 day (d), 3 days, and 15 days, respectively, for testing the strength, and the test results are shown in Table 7. The results show that when the calcium sulfate magnesium chemical double salt is adopted, the cementing material has the characteristics of quick hardening and high early strength.
Table 7 test results of strength of test pieces of chemical double salt cementing slurry in examples 7 to 9
Examples 10 to 12
In order to illustrate the water stability of the hydrate crystals in the calcium magnesium sulfate double salt cementing material of the invention, the physical double salt cementing material slurry test pieces in the examples 4-6 are cured at 25 ℃ +/-2 ℃ for 28 days, then immersed in water for 28 days, taken out and naturally dried, then the compression strength and the flexural strength of the test pieces after immersion are respectively tested, and the strength ratio, namely the softening coefficient, between after immersion and before immersion is calculated as an evaluation index of the water stability of the hydrate crystals of the cementing material, wherein the larger the softening coefficient is, the better the water stability is, and the results are shown in Table 8.
Table 8 results of the test of the softening coefficient of the physical double salt cements in examples 10 to 12
The results in Table 8 show that the softening coefficients of the test pieces of examples 10 to 12 are 1. + -. 0.1, which indicates that the calcium magnesium sulfate double salt cement slurry of the present invention can maintain its strength in water even slightly after completely hardening in air. Comparing the two XRD patterns in fig. 2, it was found that after 28 days of soaking, the hydrate crystals in the test pieces of example 12 were unchanged from those in example 6 before soaking, i.e., the hydrate crystals formed by the hydration reaction of the calcium magnesium sulfate double salt cement had high water stability, and thus were useful for the preparation of various building material products.
The above embodiments are merely representative of the present invention, which may be modified and varied in many ways. Therefore, any changes made based on the principle of the present invention should be included in the scope of protection of the present invention.

Claims (8)

1. The calcium sulfate magnesium double salt cementing material comprises the following components in parts by mass:
50-250 parts of calcium sulfate and magnesium sulfate double salt; 40-200 parts of active magnesium oxide; 50-250 parts of mineral powder; the calcium sulfate magnesium double salt is selected from one or two of calcium sulfate magnesium physical double salt and calcium sulfate magnesium chemical double salt;
the composition of the calcium sulfate magnesium physical double salt is xCaSO4•yMgSO4•zH2O, wherein in the formula, the (x/y) is more than or equal to 1 and less than or equal to 3, and the z is more than or equal to 1 and less than or equal to 3; the calcium sulfate magnesium physical double salt is prepared by the following method:
mixing industrial byproduct gypsum raw slag and magnesium sulfate, heating to 120-360 ℃ for dehydration, and physically combining calcium sulfate dihydrate in the raw slag with the magnesium sulfate to generate gypsum-based calcium-magnesium complex salt; grinding and sieving to obtain physical double salt solid powder; or
Adding dolomite powder into an industrial waste sulfuric acid solution with the mass concentration of 20-70%, and stopping the reaction until the pH value of the mixture is 4-6; evaporating free water from the mixture, and dehydrating at 120-360 ℃ to generate waste acid calcium magnesium double salt; grinding and sieving to obtain physical double salt solid powder; or
Removing SO in flue gas of industrial kiln by using dolomite, light-burned dolomite or calcined dolomite2Gas, namely obtaining mixed slurry of calcium sulfate and magnesium sulfate, and dehydrating the mixed slurry at 120-360 ℃ to generate desulfurized calcium-magnesium double salt; grinding and sieving to obtain physical double salt solid powder;
the composition of the calcium sulfate magnesium chemical double salt is Mg2Ca(SO4)3(ii) a The calcium magnesium sulfate chemical double salt is prepared by directly selecting ash slag discharged from a pressurized fluidized bed combustion furnace of a coal slime doped dolomite desulfurization process or calcining the calcium magnesium sulfate physical double salt at 725-950 ℃.
2. The calcium-magnesium sulfate double-salt cementing material of claim 1, which is characterized in that: the mineral powder is selected from at least one of fly ash, limestone powder, dolomite powder and building gypsum.
3. The calcium-magnesium sulfate double-salt cementing material of claim 1, which is characterized in that: the average particle size of the prepared physical double salt solid powder is 0.1-50 mu m.
4. The calcium-magnesium sulfate double-salt cementing material of claim 1, which is characterized in that: the industrial byproduct gypsum raw slag is at least one of phosphogypsum, titanium gypsum, citric acid gypsum, fluorgypsum, mirabilite gypsum and calcium desulphurization gypsum which are not subjected to any purification or deacidification treatment.
5. The calcium-magnesium sulfate double-salt cementing material of claim 1, which is characterized in that: the average particle size of the active magnesium oxide particles is 0.1-50 μm.
6. The method for preparing powder by using the calcium-magnesium sulfate double-salt cementing material as claimed in any one of the claims 1 to 5, which comprises the following steps: preparing each component of powder according to a designed compound salt cementing material component formula, and mixing for 4-8 minutes at a rotating speed of 60-100 revolutions per minute by using a dry powder mixer to uniformly mix the component of powder to obtain compound salt cementing material powder;
in the components of the double-salt cementing material, the physical double salt of calcium sulfate and magnesium sulfate and the chemical double salt are added independently or mixed; the active magnesium oxide is selected from one or a mixture of two or more than two of light-burned magnesium oxide powder, light-burned dolomite powder or industrial active magnesium oxide.
7. The method for preparing the calcium sulfate magnesium double salt cementing material slurry comprises the following steps: preparing powder of each component according to a designed formula of the components of the double-salt cementing material; metering and pumping clear water into a stirrer; adding the double-salt cementing material powder prepared in the claim 6 into a stirrer, and uniformly stirring at a rotating speed of 100-120 r/min to obtain calcium sulfate magnesium double-salt cementing material slurry.
8. The application of the calcium sulfate magnesium double salt cementing material is that the slurry of the calcium sulfate magnesium double salt cementing material prepared in the claim 7 is mixed with mineral powder and fiber, and is molded into a blank after being stirred uniformly, and the blank is coagulated and hardened at normal temperature or in the environment below 100 ℃ to prepare products used in the fields of buildings, building materials and other industries; the mineral powder is at least one of limestone powder, dolomite powder and talcum powder; the fiber is at least one of glass fiber, PVA fiber and PP fiber; the molding is realized by adopting the modes of pouring, extruding and rolling through a designed die.
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